Some products, especially fluids, are sold in containers in which they slowly release gases resulting in an overpressure in the interior of the container. This applies for instance to some bleaching products containing hydrogen peroxide, chlorine or chlorine doners percarbonate or perborate. In order to prevent such gas-releasing products from causing an inappropriately high internal overpressure in the container containing said products, said container is often provided with a so-called venting cap, i.e. a self-sealing cap ensuring a venting of the container when the internal overpressure exceeds a predetermined amount.
A wide range of various venting caps are known. U.S. Pat. No. 3,067,900 discloses a plastic screw cap comprising a thin resilient frusto-conical sealing member, which extends downwards and outwards from the bottom side of the upper wall of the cap so as to resiliently and sealingly engage the pouring lip of the neck of the container to be closed.
Furthermore, EP-B1-0 267 748 discloses a screw cap provided with an upper flange extending inwards from the skirt and connected through a number of resilient spokes to a disc-shaped, centrally arranged sealing means; When the cap is screwed down, the sealing means sealingly abut the edge of the neck of the container to be closed. When the internal overpressure increases sufficiently, the sealing means is forced upwards and out of engagement with the container with the result that said container is vented. Subsequently, the sealing means returns to the sealing position.
Several of the known venting caps are encumbered with the draw-back that they do not provide a specific venting pressure, and/or that they are not able to completely seal the container after the first venting. Such problems apply in particular to foaming, tacky and/or viscous fluids.